The present invention relates to a process and to an apparatus for the production of back-foamed products and in particular, upholstery with back-foamed covers, particularly for seats in motor cars. In the process, a piece of material for the cover is placed on a mold half and pressed against the edge of the mold cavity. A vacuum is then applied to the cavity, and the material is sucked into the cavity against the pressure acting on it and is fitted to the contour of the cavity. A foamable reaction mixture is then introduced into the mold cavity and the complete seat cushion is removed when the foam has hardened.
In order to produce a piece of upholstery with visually perfect contours, it is important to ensure that when the material for the cover is sucked into the mold cavity by the vacuum, it is placed into position in such a manner that it is either free from folds or has predetermined folds in particular positions. This necessitates controlled sliding of the cover into position. This sliding control is obtained by using a stretching frame which exerts sufficient force to press the material for the cover against the edge of the lower mold half surrounding the mold cavity.
It has already been attempted to control this sliding movement of the cover under the frame by means of a film of air under pressure (German Patent 3,034,973). This method has not always been found satisfactory in practice and difficulties occur particularly if the material of the cover is not stretchable.
The problem lies in improving the control of the contact pressure acting on the material of the cover as it slides over the edge surrounding the mold cavity so that the material will slide into position to fit firmly against the wall of the cavity at every point.